After the last renter moved out you can add the cost of improvements to your basis but cannot deduct rental expenses because the property was not rented or available. You need to file a 3115 with your 2020 return.....you don't amend your 2019 return for this.....and you will get a wash since the foregone depreciation deductions will be recovered while your basis will be lowered to the same extent. Get a tax pro no matter what.
